1. Field of the Invention
The present invention relates to a viscosity detector including a liquid detector provided at the end of a vibration transmission shaft.
2. Brief Description of the Prior Art
The inventors of the present invention has already proposed a viscosity detector having a liquid detector disposed at the end part of a vibration transmission shaft. The liquid detector is vibrated in a same direction in a liquid by driving the vibrating shaft about an axis line with a piezoelectric type vibrator to sense viscous resistance. The viscosity of the liquid is detected based on a variation of the vibration due to the viscous resistance as disclosed in U.S. Pat. No. 4,811,593 and U.S. Pat. No. 5,228,331.
Since the viscosity detector of the aforementioned type employs a system which vibrates the vibration transmission shaft and the liquid detector about an axis line at a resonance frequency by a vibrator which is adapted to vibrate in a circular direction, the vibrating shaft is supported in the vicinity of a node of the resonance, and the detector is correctly vibrated by fitting the vibration shaft to a housing of the viscosity detector or a container of a liquid to be measured.
However, the conventional viscosity detector has a problem in that the node of the resonance can be dislocated from the intended position due to a fabrication error, or an assembling error of the vibration transmission shaft, with the bearing portion and the liquid detector. The errors will cause the node of the resonance to be incoincident with the bearing portion, resulting in extremely degraded performance of the viscosity detector.
This problem also results in a viscosity detector which will not necessarily maintain the reliability of the design during construction or while in use.